Infection is the leading cause of morbidity and mortality in patients with acute leukemia and a major cause in other types of advanced malignancies. The aims of this project are to 1) catalogue and identify the infections manifest both clinically and postmortem, 2) identify the predisposing factors which have contributed to the specific type of infection, 3) evaluate new techniques for more rapid and/or accurate diagnosis of infection. Beginning July 1, 1970, each patient with suspected infection has been seen by one of the investigators who examine the patient and reviews the chart, both initially and throughout the course of the infection. Detailed records are kept of history, examination, laboratory data, etc. Similar details are obtained on infections at the time of postmorten examination. Review of all infections occurring among all patients treated for cancer by a small number of physicians under protocol conditions on a single hospital floor over a 5-year period has provided a unique opportunity to detect differences in infection type and incidence among different classes of tumor and to better understand the predisposing factors to each class of infections.